ci: configure additional CI jobs & bring linter settings in compliance with OSS template

[jtieri]

This PR adds some additional CI jobs:

• Codespell (which checks for grammar mistakes)
• Dependabot (which monitors for out of date deps and security vulnerabilities)
• Mergify (which can be used for automatically backporting commits across maintained versions)
• CodeQL (which looks for code smells, security vulnerabilities, etc.)
• Markdown Link Checker (which looks for broken markdown hyperlinks)
• Title Format (which enforces conventional commits in PR titles)

It also tweaks the golangci-lint settings to be in compliance with the OSS template.

All repo settings should also be in compliance with the OSS template now, besides for configuring the few extra CI jobs to have passing statues before PRs can be merged.

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TODO: Do we bring the build & test CI job and the goreleaser CI job into compliance with the OSS template or do we leave the currently configured settings?